Colorado CDL: Air Brakes Practice Test

Not quite. The answer is controls the air pressure to operate the brakes.

When you press the brake pedal in a CMV equipped with air brakes, the foot valve underneath the pedal opens to allow compressed air to flow to the brake chambers. The brake chambers exert mechanical force to operate the foundation brakes.

Not quite. The answer is 2 psi per minute.

Perform the first test of air leakage with the engine off and the brakes released. The air-loss rate should be less than 3 psi per minute for a combination vehicle and less than 2 psi per minute for a bus or straight truck. After you've tested this initial drop, now test air leakage with the engine off and the foot brake fully applied. This time, the air-loss rate should be less than 4 psi per minute for a combination vehicle and less than 3 psi per minute for a bus or straight truck.

Not quite. The answer is Typically, one brake system operates the brakes on the front axle, and the other system operates the brakes on the rear axles.

A dual air brake system has two separate air brake systems, each with its own air tanks, hoses, lines, etc. Both systems are controlled by the one brake pedal. Typically, the primary system operates the brakes on the rear axle, and the secondary system operates the brakes on the front axle (and possibly one rear axle as well).

Not quite. The answer is All of the above are true.

A dual air brake system is a system designed for safety and used on most heavy-duty vehicles. It uses one set of controls. Typically, the "primary" system operates the regular brakes on the rear axle, and the "secondary" system operates the regular brakes on the front axle.

Not quite. The answer is does all of the above.

The tractor protection valve protects your air brake system by providing the air supply, closing automatically if the air supply drops too low, and closing if you apply the parking brakes on your vehicle.

Not quite. The answer is a Class A CDL without an air brakes restriction.

To legally pull a trailer whose gross vehicle weight rating (GCWR) exceeds 10,000 pounds, you'll have to obtain a Class A CDL. If you don't pass a knowledge test on air brakes, your CDL will include a restriction limiting you to driving only vehicles without air brakes.

Not quite. The answer is spring pressure.

Federal safety regulations require buses and trucks to have parking and emergency brakes that don't rely on compressed air or hydraulic fluid to work (because these can leak away). Hence, the parking and emergency brakes rely on mechanical force such as springs.

Not quite. The answer is so you only have to apply the brakes just hard enough to feel a definite slowdown.

When starting down a downgrade, shift into a low gear and use engine braking to slow your vehicle. Apply the brakes just enough to keep your vehicle near your safe speed.

Not quite. The answer is Whenever your vehicle is parked

You should always use your parking brake except when the brakes are very hot or they are wet and at risk of freezing.

Not quite. The answer is 100 psi.

A dual air brake system has two separate air brake systems. Typically, the primary system operates the brakes on the rear axle(s), and the secondary system operates the brakes on the front axle (and possibly one rear axle). Before driving a vehicle with a dual air brake system, let the air compressor build up a minimum of 100 psi pressure in each of the two brake systems.

Not quite. The answer is All of the above

Fade and fail are usually due to incorrect use of the brakes that causes excess heat. This may be caused by incorrect brake adjustment, not enough reliance on engine braking, excessive use of the service brakes, or another mechanical factor or human error.

Not quite. The answer is braking effect of the engine.

Going down a hill, you should keep your engine in a low gear to keep your speed low, and use the air brakes as a supplemental tool to slow down.

Not quite. The answer is service

Air brakes are really three braking systems in one: the emergency brake, the parking brake, and the service brake. As these names suggest, when you depress the brake pedal in normal driving, it's the service brake system that applies the brakes.

Not quite. The answer is 45

In dual air systems with minimum-sized air tanks, the pressure should build from 85 to 100 psi within 45 seconds. (With larger air tanks, it can take longer. Check the manufacturer's specifications for the expected amount of time.) If it takes longer than it should, there may be a problem with your system that may cause you to lose air pressure while you're driving.

Not quite. The answer is Bring the vehicle to a safe stop and continue only after the system is fixed.

A dual air brake system has two separate air brake systems. Typically, the primary system operates the brakes on the rear axle(s), and the secondary system operates the brakes on the front axle (and possibly one rear axle). If one of these two systems loses air pressure (causing the low air pressure warning), either the front or the rear brakes won't work properly. As a result, your vehicle's braking distance will increase. If this happens, stop your vehicle and get the system fixed.

Not quite. The answer is At the end of each working day

Oil and water can start to collect in the bottom of an air tank and can cause brake failure if it's not drained. Unless your vehicle automatically drains the air tanks, you should drain them at the end of each working day so the moisture and oil will not freeze or coagulate and cause your brakes to fail.

Not quite. The answer is depress the brake pedal as hard as you can, release the brakes when the wheels lock, and apply the brakes again when the wheels start to roll.

To stop with stab braking, brake hard, release the brakes once the wheels lock, and then brake hard once the wheels start to roll again. (Clearly, this method won't work if your vehicle has antilock brakes, because the wheels won't lock. Use controlled braking instead.)

Not quite. The answer is Either the front or rear brakes will not be fully operational.

A dual air brake system has two separate air brake systems, each with its own air tanks, hoses, lines, etc. Typically, one system operates the brakes on the rear axle(s), and the other system operates the brakes on the front axle. If one of the systems loses air pressure, either the front or the rear brakes won't work properly. As a result, your vehicle's braking distance will increase. If this happens, stop your vehicle and get the system fixed. Continued braking would soon cause the spring brakes to come on.

Not quite. The answer is To prevent a buildup of ice in the air brake system

When the air compressor runs, an alcohol evaporator puts alcohol vapor into the air brake system to help prevent water in the lines or valves from freezing. Ice in the lines or valves can cause them to stop working.

Not quite. The answer is To avoid injury from high-pressure air and debris

Compressed air may be exhausted from several different ports in the air braking system. This air travels at a very high speed from the vehicle and carries moisture, oil, dirt, and dust. It can be dangerous if it hits your eyes or ears. Know the location of all air exhaust ports so you can keep away from them, such as when you're draining the air tanks.